In gas turbines with a plurality of burner stages which are in operation at the same time, it is known to realize feed of the burner stages with fuel via two or more regulated control valves and ring mains in each case, depending upon the number of “burner stagings” (see, for example, WO-A1-2005/093327). Such an arrangement is exemplarily reproduced in a much simplified form in FIG. 1. The fuel distribution system 10 of FIG. 1 comprises a plurality of burner stages of which the two first burner stages 11 and 12 are explicitly shown. Each of the burner stages comprises one or more burners 13 or 14 which are connected to a common fuel ring main 15 or 16. Each of the fuel ring mains 15, 16 is connected via a distribution line 19, 20, 21 to a common fuel feed line 18 via which the fuel is supplied for the entire burner system. Control valves 22, 23, 24, which are connected to a control unit 17 and are controlled or regulated by the control unit 17, are arranged in each case in the distribution lines 19, 20, 21.
Depending upon the operating point, the required fuel mass flow for the respective burner stage 11, 12 is adjusted via the control valves 22, 23, 24. In this case, a fuel feed stage at low load and when starting the gas turbine is normally designed so that fuel-rich zones are locally established in the burner flow field and ensure a broad operating field of the burner. In the higher load range, this fuel feed is noticeably reduced in order to realize low emissions values (see: EP-B1-0 704 657 and WO-A1-01/96785).
The fuel feed which is established for the lower load range in this case is to preferably have higher pressure loss with regard to the fuel feed so that in full load operation with low throughputs a sufficient fuel distribution across the burners can be ensured. On the other hand, during ignition and when starting the gas turbine a sufficiently smaller fuel mass flow has to be established in order to avoid over-firing of the turbine. Since a multiplicity of control valves have to be adjusted and regulated at the same time, instabilities in the controlling behavior of the fuel feed may occur, which can lead to increased pollutant emission and pulsations in the combustion chamber.